Connection of internally lined pipelines

ABSTRACT

An insert ( 10 ) for use in connecting two length of pipe each of use has a plastic liner. The insert consists of an inner tubular member ( 12 ) of plastics material for connection at either end to the liners of two pipe length&#39;s, an insulating sleeve ( 14 ) surrounding a central portion of the inner tubular member ( 12 ) and a ring ( 16 ) of heat-resistant material overlying part of the insulating sleeve ( 14 ) to be positioned, in use, beneath a location at which the pipe length or butt welded. The insulating sleeve ( 14 ) comprises an insulating material ( 22 ) which is at least partially enclosed with a sheath ( 24 ) such that the sheath ( 24 ) can be mechanically connected to the interior of one said pipe length.

This invention relates to pipelines which are lined with a plasticsmaterial.

Pipelines are constructed by first forming lengths or “stalks” of pipe,and subsequently joining the stalks together. The stalks may be joinedin the field for a land-based pipeline. for a subsea pipeline, thestalks may be joined on a lay barge, or may be joined while the pipe isbeing reeled onto a reel laying vessel.

In many applications a metal, typically a steel, pipeline must be linedwith a plastic liner in order to prevent corrosion of the internalsurface of the pipe because of the nature of the fluid to be transportedand on conditions of use such as pressure and temperature. Whenconnecting stalks of lined pipe together, it is necessary to ensure thatthe corrosion protection provided by the liner is continuous across theconnection.

In onshore use, it is common to connect together stalks of pipe byflanged connections, with the liner material being trapped between theflanges. However, in some land based applications and in many subseauses, it is not possible to use flanged connections. This isparticularly the case when laying undersea pipelines by reel-layingmethods.

In these cases it is necessary to connect the pipe stalks by buttwelding, and to do so in such a way that the plastic liner is notdegraded by the heat of welding. Various means of achieving this havebeen proposed in the prior art.

It is also known to use plastic liners which are provided on their outerfaces with continuous longitudinal grooves. This is done because gaswithin the transported fluid can permeate through the liner andaccumulate at the liner/pipe interface. The grooves allow the gas totravel along the interface to some point where a gas drawoff is providedthrough the pipe. Prior art methods of joining lined pipe stalks do notpermit such grooves or equivalent gas seepage paths to extend across thejoin.

In the case of reeled pipeline for offshore applications, the assemblyof the stalks is made during reeling of the pipe onto the vessel. It istherefore important to reduce the time taken for connecting the stalks,in order to minimise the immobilisation of the vessel.

U.S. Pat. No. 5,998,691 shows a method of connecting stalks of linedpipe which makes use of pup pieces welded within the ends of the pipestalks. This method requires continuous corrosion-resistant welds to bemade between the pipes and the pup pieces. This method is complicated toimplement and takes time. Also, it cannot provide gas drainage groovesextending across the join.

U.S. Pat. No. 5,348,211 also relies on the use of metal inserts weldedinto the pipe stalk ends, with similar disadvantages.

EP 0,366,299 shows an arrangement using a thermoplastic insert whichcarries a ceramic ring on top of which welding is performed, insulationbeing provided between the ceramic ring and the thermoplastic material.However, the arrangement disclosed in this document has the disadvantagethat the location of the ceramic ring can vary; this is because theliners and the insert are typically joined under tension, and whenabutting the external pipe there can be no assurance that the liner haskept its position. Also, during service the liner can move within thepipe. It is therefore difficult to ensure that the ring is positionedunder the pipe welding location in all circumstances. Also, this priorart considerably reduces the size of the internal bore while keeping thethickness of the liner at the connection, and it cannot be implementedwith a grooved liner.

A primary object of the present invention is to provide a method ofjoining lined pipelines, and an insert for use in said method, whichgive a simple and quick connection with reduced risk of damage to theliner. Preferred forms of the invention are also capable of providingconnection between grooved liners.

The present invention provides an insert for use in connecting twolengths of pipe each of which has a plastics liner, the insertcomprising:

-   -   an inner tubular member of a plastics material for connection at        either end to the liners of two pipe lengths;    -   an insulating sleeve surrounding a central portion of the inner        tubular member; and    -   a ring of heat-resistant material overlying part of the        insulating sleeve to be positioned, in use, beneath a location        at which the pipe lengths are butt welded;    -   the insulating sleeve comprising an insulating material which is        at least partially enclosed by a sheath such that the metal        sheath can be mechanically connected to the interior of one of        said pipe lengths.

The invention further provides a method of connecting a first pipecontaining a first liner to a second pipe containing a second liner, themethod comprising the steps of:

-   -   providing an insert as defined above;    -   stretching the first liner so as to extend from an end of the        first pipe;    -   cutting the extended portion of the first liner at a location        calculated to cause the cut end of the first liner, upon release        of the stretching force, to lie at a given position within the        first pipe;    -   securing one end of the inner tubular member of the insert to        the cut end of the first liner;    -   applying a bonding material to the insulating sleeve;    -   releasing the stretching force to cause the cut end of the first        liner to retract to said given position and the bonding material        to bond to the internal surface of the first pipe;    -   stretching the second liner so as to extend from an end of the        second pipe;    -   cutting the extended portion of the second liner at a location        calculated to cause the cut end of the second liner, upon        release of the stretching force, to lie at a given position        within the second pipe;    -   securing the other end of the inner tubular member of the insert        to the cut end of the second liner;    -   releasing the stretching force to cause the cut end of the        second liner to retract to said given position within the second        pipe while bringing the ends of the first and second pipes into        abutment; and    -   welding the abutting ends of the first and second pipes        together.

Preferred features and advantages of the invention will be apparent fromthe following description and the claims.

An embodiment of the invention will now be described, by way of exampleonly, with reference to the drawings, in which:

FIG. 1A is a general arrangement, shown in cross-sectional sideelevation, of an insert forming one embodiment of the present invention;

FIG. 1B is a cross-sectional end view taken on the line B-B of FIG. 1A;

FIG. 2A is a more detailed sectional view of a sleeve forming part ofthe insert of FIG. 1;

FIGS. 2B and 2C are enlarged views of details of FIG. 2A;

FIGS. 3A and 3B are side and end views, respectively, of a tubularmember forming part of the insert of FIG. 1; and

FIGS. 4A to 4G are schematic side views illustrating successive steps inusing the insert of FIG. 1 to join two pipe stalks.

Referring to FIGS. 1 to 3, an insert 10 for use in joining two lengthsof pipe comprises an inner tubular member 12 having a central recess inwhich is received a sleeve 14. The sleeve 14 in turn has a peripheralannular groove in which is received a non-metallic heat resistantelement such as a ceramic ring 16. The insert 10 is intended for use injoining pipes having plastic liners, for example of high densitypolyethylene (HDPE) or fluorocarbon polymer, and the tubular member 12is formed of a material matching the liners. One suitable material forthe tubular member 12 is “Rilsan” polyamide by Atofina. The ceramic ringmay, for example, be of Gullco “Katbac” material.

As best seen in FIG. 2, the sleeve 14 comprises a thermal insulationmaterial 22 enclosed within a sheath 24. The insulation material ispreferably a compressible material, for example a compressiblemicroporous or insulation foam; one example is a microporous foam havinga density of 160-210 kg/m³. The sheath 24 in this embodiment isfabricated from stainless steel 1 mm thick, the parts being brazed atthe locations identified at 26. Other metallic materials, for examplecarbon steel, or non-metallic materials may be used. In some embodimentsthe sheath is sufficiently thin that in use of the eventual pipeline theworking pressure will compress the sheath 24 and insulating material 22,thereby reducing the extent to which the insert 10 reduces the workingbore of the pipeline. Such compression is assisted by the provision ofend clearances 28 within the sheath 24.

In alternative embodiments of the invention, the sheath 24 can bedesigned to withstand the working pressure and so it can be fabricatedof high strength steel for example. In these embodiments, the internaldiameter of the bore of the pipeline will experience a reduction throughthe connection but the risk of damaging the tubular body 12 of theinsert 10 due to the collapse of the sleeve 14 will be reduced oreliminated.

As best seen in FIGS. 2 and 3, one end of the sleeve 14 has the sheath24 formed at 30 to present an acute angle α which may typically be 45°.The tubular member 12 has a correspondingly angled annular recess 32 inwhich the end 30 of the sleeve 14 is received.

The sheath 24 allows the sleeve 14 to be bonded to the host pipe duringthe connection process, preferably by use of an epoxy adhesive. The useof bonding obviates the need for welding the sleeve in place, thusreducing the risk of introducing a fatigue initiation point. Thisbonding ensures that the heat resistant element is placed at the correctlocation during external pipe welding operations.

Furthermore, due to the boding of the sheath 24 to one stalk of pipe,the insert is anchored in the host pipeline at each connection location.the acute angle α assists in anchoring the liner during installation andin service by reducing the risk of the liner pulling through theinsulating sleeve.

The insert 10 may suitably be assembled by forming the tubular member 12in two parts which are joined by fusion along the line 18 after thesleeve 14 and ring 16 have been positioned.

In the illustrated embodiment, the tubular member 12 is formed withgrooves, in this embodiment six grooves 20, which extend along itslength and beneath the sleeve 14. The provision of the grooves 20 allowsthe insert 10, when used with grooved pipe liners, to provide a gasdrain path extending through the connection. In alternative embodimentsof the invention the grooves 20 may be omitted, or may be replaced withlongitudinal bores extending within the insert body which may beadvantageous in reducing strains on the insert material. In theillustrated embodiment, the sheath 24 is useful in protecting thegrooves 20 from the insulation material 22. In this case, the sleeve 14and its sheath 24 can be calculated to withstand the bore workingpressure in order to protect the grooves 20.

FIG. 4 shows one example of the method of the invention, in which theinsert 10 is used in joining a first pipe stalk 40 having a plasticliner 42 to a second pipe stalk 44 having a plastic liner 46. The methodexample will be described herein with reference to use with a reelpipelaying ship, but it will be apparent that a similar method may beused in other applications.

The first stages shown in FIGS. 4A-4C are carried out at the spoolbasewhere the pipe stalk 40 has been prepared by welding together lengths ofpipe and pulling in the liner 42. The liner 42 is pulled through thestalk (FIG. 4A) and then the tension released.

The liner 42 is then extended under tension and released to establishwhere a cut must be made to produce a cut end at a desired locationwithin the pipe stalk 40. Then, as seen in FIG. 4B, the liner 42 isextended by the required amount and clamped in position by an internalclamp 48 and the liner 42 is cut at 50.

The insert 10 is then positioned abutting the cut liner 42 (FIG. 4C),and the end of the member 12 is fused to the cut end of the liner 42.Epoxy resin is applied to the end of the sleeve 14 facing the pipe stalk40. The clamp 48 is then released, allowing the liner. 42 to retractdrawing the insert 10 partially within the first pipe stalk 40, and theepoxy resin bonds the insert in position within the pipe stalk 40.

The pipe stalk 40 is now reeled onto the reel vessel with the endillustrated extending from the reel.

FIG. 4D shows the leading end of the next pipe stalk 44. The liner 46 isextended under tension and released to allow the position for therequired cut to be established. Then, the liner 46 is extended andclamped by an external clamp 51, and the liner 46 is cut at 52 suchthat, on release, the cut end will lie at 54 within the pipe stalk 44.

The next steps will usually be performed in the tie-in shed adjacent thevessel as the stalk 44 arrives. The liner 46 is extended and held by theclamp 51 (FIG. 4E) while the liner 46 is aligned with the insert 10 andthe liner 46 is fused to the tubular member 12 at 52. After removing theexternal fusion bead (the internal bead can remain), the clamp 51 isremoved and the stalks 40 and 44 are closed together (FIG. 4F) as theliner retracts.

The ends of the pipe stalks are then aligned for butt welding (FIG. 4G),the weld is made, and the joint is tested.

A preferred feature of the insert 10 is that it is designed to partiallycollapse or compress under the working pressure of the eventualpipeline, due to the design of the insulating sleeve. The exemplaryconstruction detailed above is suitable for this purpose in a typicalsubsea pipeline. The encapsulated insulating material collapses,allowing the body of the insert to move radially outward. This featureminimises the reduction of flow area in the pipeline caused by theinsert. Where a grooved liner is being used, the metal sheath willprevent the grooves being obstructed by the insulating material. Thepresent invention also makes it possible to provide a join between pipestalks which has bending characteristics similar to those of the pipe.

Modifications may be made to the foregoing embodiment within the scopeof the invention. For example, the sleeve could be only partially, asopposed to entirely, encased in metal but it is desirable to provide ametal portion at least in an area suitable for bonding to the pipe. Thiscould be done by having metal covering to the ends and the outer surfaceonly, or to the ends, the inner surface and end portions of the outersurface. An inner metallic portion is useful in maintaining the groovesopen.

It is also possible to incorporate material in the insert which acts asa reflector for radiographic examination, which can be useful inchecking the positioning of the insert within the pipe.

1. An insert (10) for use in connecting two lengths of pipe each ofwhich has a plastics liner, the insert comprising: an inner tubularmember (12) of a plastics material for connection at either end to theliners of two pipe lengths; an insulating sleeve (14) surrounding acentral portion of the inner tubular member (12); and a ring (16) ofheat-resistant material overlying part of the insulating sleeve (14) tobe positioned, in use, beneath a location at which the pipe lengths arebutt welded; the insulating sleeve (14) comprising an insulatingmaterial (22) which is at least partially enclosed by a sheath (24) suchthat the sheath can be mechanically connected to the interior of one ofsaid pipe lengths.
 2. An insert (10) according to claim 1, in which theinsulation material (22) is totally enclosed by the sheath (24).
 3. Aninsert (10) according to claim 1, in which the sheath (24) is a metalsheath.
 4. An insert (10) according to claim 1, in which the length,thickness and materials of the insulating sleeve (14) are chosen suchthat the temperature at the inner tubular member (12) during welding isbelow a predefined temperature.
 5. An insert (10) according to claim 1,in which the insulating sleeve (14) is adapted to partially collapseunder the application of pipeline pressure in order to reduce theintrusion of the insert (10) into the pipeline bore.
 6. An insert (10)according to claim 1, in which the insulating sleeve (14) has one axialend formed at an acute angle, which end is received in a correspondingannular groove in the inner tubular member (12).
 7. An insert (10)according to claim 1, in which the outer surface of the inner tubularmember (14) is formed with a plurality of grooves (20) to provide adrainage path for gases.
 8. An insert (10) according to claim 1, inwhich said insulating material (22) is a foam.
 9. A method of connectinga first pipe (40) containing a first liner (42) to a second pipe (44)containing a second liner (46), the method comprising the steps of:providing an insert (10) in accordance with claim 1; stretching thefirst liner (42) so as to extend from an end of the first pipe (40);cutting the extended portion of the first liner (42) at a locationcalculated to cause the cut end of the first liner (42), upon release ofthe stretching force, to lie at a given position within the first pipe(40); securing one end of the inner tubular member (12) of the insert(10) to the cut end of the first liner (42); applying a bonding materialto the insulating sleeve (14); releasing the stretching force to causethe cut end of the first liner (42) to retract to said given positionand the bonding material to bond to the internal surface of the firstpipe (40); stretching the second liner (46) so as to extend from an endof the second pipe (44); cutting the extended portion of the secondliner (46) at a location calculated to cause the cut end of the secondliner (46), upon release of the stretching force, to lie at a givenposition within the second pipe (44); securing the other end of theinner tubular member (12) of the insert (10) to the cut end of thesecond liner (46); releasing the stretching force to cause the cut endof the second liner (46) to retract to said given position within thesecond pipe (44) while brining the ends of the first and second pipes(40, 44) into abutment; and welding the abutting ends of the first andsecond pipes (40, 44) together.
 10. A method according to claim 9, inwhich the bonding material is epoxy resin.
 11. A method according toclaim 10, in which the epoxy resin is applied to the sheath (24) of theinsert (10).
 12. A method according to claim 9, in which, before thefirst liner (42) is stretched and cut, the liner (42) is first stretchedand released to allow estimation of the cutting position required tobond the insert in a position such that the butt weld overlies theceramic ring (16).